1. Field of the Invention
The present invention relates to a hard coat layer comprising a transparent plastic film having thereon a curable layer formed of a curable composition containing polyfunctional acrylate and polyrotaxane. More specifically the invention relates to a hard coat film high in surface hardness having such a hard coat layer having a thickness of 10 μm or more, an antireflection hard coat film having the hard coat film as the substrate, and a polarizing plate and an image display using the antireflection hard coat film.
2. Description of the Related Art
Antireflection films comprising a transparent plastic film substrate having thereon an antiglare hard coat layer (what is also called an antiglare film) and a hard coat layer and a low reflectance layer by lamination are arranged on the surfaces of various displays such as a liquid crystal display (LCD), a plasma display panel (PDP), an electroluminescence display (ELD), and a cathode ray tube (CRT) for the prevention of contrast reduction by reflection of outer light and mirroring of images due to surface scattering and low surface reflection.
In recent years, image displays mounting an antireflection film have been spread along with the price reduction of liquid crystal televisions. With such tendency, the cases where the mounted antireflection films are exposed to various environments with the image displays have increased. In particular, such cases have increased where antireflection films are handled like braun tube televisions having a glass surface, and the possibility that the surfaces of liquid crystal displays are scratched is increased. Accordingly, the antireflection film used as the outermost surface of a liquid crystal display is required to have high physical strength (scratch resistance and the like) in addition to high improving effect of visibility that has so far been required.
In recent years, a novel kind of gel by a new technique not being classified to any of physical gel and chemical gel, that is, “gyrate gel or topological gel”, is proposed, and polyrotaxane is used in such gyrate gel. Polyrotaxane is a conceptual compound comprising cyclic compounds and a straight chain polymer penetrating a plurality of these cyclic compounds, and having a structure of capping both terminals of the straight chain polymer.
For example, Japanese Patent No. 2810264 discloses polyrotaxane using α-cyclodextrin as the cyclic compound and polyethylene glycol as the straight chain polymer.
Japanese Patent No. 3475252 discloses crosslinked polyrotaxane that is applicable to gyrate gel by crosslinking of a plurality of polyrotaxanes. Since the crosslinked polyrotaxane is such that cyclic molecules penetrated by straight chain molecule are capable of moving along the straight chain (a pulley effect), the crosslinked polyrotaxane has viscoelasticity, and even when tensile force is applied, the tensile force can be evenly dispersed by the pulley effect. Accordingly, the crosslinked polyrotaxane has excellent characteristics such that cracks and scratches are hardly caused unlike conventional crosslinked polymers.
The researches of applications of these polyrotaxane and crosslinked polyrotaxane to various fields have been progressed, but the application of these polyrotaxanes to the hard coat layer of the hard coat film for a liquid crystal display has not been advanced.
In connection with the application of polyrotaxane to coatings, JP-A-2007-099989 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.) discloses a coating containing polyrotaxane for automobiles. However, since the support of a hard coat film for a liquid crystal display is a plastic film having flexibility, problems such as curling and brittleness are important. Contrary to this, the support of automobiles is a steel plate having rigidity, so that the improvements of curling and brittleness have not been suggested at all.